1 Preventive and Community Dentistry Unit, Department of Dental Clinical Specialties, Faculty of Dentistry, Complutense University of Madrid, Madrid, Spain. Electronic address: angelors@ucm.es.
2 Department of Nursery and Stomatology, Faculty of Dentistry, Rey Juan Carlos University, Madrid, Spain.
3 Preventive and Community Dentistry Unit, Department of Dental Clinical Specialties, Faculty of Dentistry, Complutense University of Madrid, Madrid, Spain.